Scolex

Quinacrine concentrates in the scolex of the parasite and causes the muscles needed for holding onto the intestinal wall to relax. The worms are stained yellow and pass from the body, still aUve. Quinacrine can intercalate with DNA and inhibit nucleic acid synthesis. It creates fluorescent bands in deoxyadenylate—deoxythmidylate-rich regions of DNA and has been used as a stain in the study of human genetics. 

Niclosamide inhibits oxidative phosphorylation and stimulates adenosine tripho-sphatese activity in the mitochondria of cestodes, killing the scolex and proximal segments of the tapeworm both in vitro and in vivo. The scolex of the tapeworm, then loosened from the gut wall, may be digested in the intestine and thus may not be identified in the stool even after extensive purging [90,91], Niclosamide is not appreciably absorbed from the gastrointestinal tract [92,93] and the side effects have primarily been limited to gastrointestinal symptoms. 

The drug affects the scolex and proximal segments of the cestodes, resulting in detachment of the scolex from the intestinal wall and eventual evacuation of the cestodes from the intestine by the normal peristaltic action of the host s bowel. Because niclosamide is not absorbed from the intestinal tract, high concentrations can be achieved in the intestinal lumen. The drug is not ovicidal. 

The majority of adult tapeworms have an attachment region, the scolex, from which a series of proglottids develop, giving the animal a segmented appearance proglottids distal to... 

Fig. 1.10. Interrelationships of the Cestoda adapted from Olson ef a/. (2001) after Hoberg ef a/. (2001b). The serial repetition of gonads appeared in cestode evolution with the appearance of the Spathebothriidea proglottization immediately after that with the emergence of difossate lineages and then the majority of lineages with a four-part scolex appearing thereafter.

The intestinal immune response, or more appropriately the immunophysiological response, to tapeworms can be considered in two categories (i) creation of an inhospitable environment and (ii) active humoral events aimed at destruction of the tegument, destro-bilization and scolex detachment. We provide a brief overview of the response to cestodes, with pertinent species-specific and life-cycle stage-specific events given in the following section. 

The various forms of cestode scolex or holdfast are well known and are described in standard texts (32, 345,800,933). In general, the morphology... 

The bothriate type of scolex consists typically of a pair of shallow,... 

Glands in the rostellar region of the scolex of a number of Cyclo-phyllidea, e.g. Hymenolepis spp., Taenia solium, T. crassiceps, Davainea... 

Table 2.2. Species of adult cestodes with scolex glands, investigated by Kuperman Davydov (19826).

Pig. 2.6. Three types of secretory mechanisms found in the scolex glands of adult cestodes. (After Kuperman Davydov, 19826.)... 

In cestodes, most, perhaps all, of the neural elements are found in the ganglia of the scolex and the main nerve tracts. In these, the cell bodies are arranged peripherally around a core made up of a tangled mass of neuronal processes often referred to as neurites because it is impossible to distinguish between axons and dendrites. This mass constitutes the so-called neuropile . Like all differentiated cells in cestodes - and probably in all invertebrates - nerve cells are incapable of mitosis and hence new nerve cells must arise directly from the germinative ( = stem) cells (276). In D. dendriticum, the neuropile is composed of a dense network of unmyelinated nerve fibres with no extracellular stroma between the fibres (277). The fibres differ mainly in the content of different types of vesicles, which can be dense-core, small clear or large clear vesicles. The structure of synapses is discussed further on pp. 25—7. 

In the scolex ganglion of the tetraphyllid Pelichnobothrium speciosum, where unipolar and multipolar neurones are found, the nerve cell processes have been reported as forming tight junctions which cannot be interpreted as synaptic contacts 260) this anomalous observation clearly requires confirmation. 

Fig. 2.12. Scolex of Diphyllobothrium dendriticum plerocercoid. The neural elements have been labelled with growth hormone releasing factor (GRF), a vertebrate neuropeptide. In the main nerve cord (n) one GRF-immunoreactive cell body can be seen (large arrow) in the peripheral nervous system (P) several GRF-immunoreactive cells bodies occur (large arrows). The small arrows point to nerve terminals beneath the basal lamina of the tegument along the inner border of the bothridia. Sections stained with Stemberger s immunoperoxidase-antiperoxidase (PAP) technique. (Courtesy Dr Margaretha K. S. GustafFson.)...

Some species, e.g. E. granulosus, will evaginate their scolex in saline alone, but this process may be slow or only temporary, and such a response would be inadequate to bring about the rapid evagination and subsequent attachment to the mucosa which is required if the larva is to avoid being swept away by the continuous peristaltic movements of the gut. The addition of bile, however, produces almost instant evagination in most... 

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